During patient care, it is important to know the composition of the patient's blood. Knowing the composition of the patient's blood can provide an indication of the patient's condition, assist in patient diagnosis, and assist in determining a course of treatment. One blood component in particular, hemoglobin, is very important. Hemoglobin is responsible for the transport of oxygen from the lungs to the rest of the body. If there is insufficient total hemoglobin or if the hemoglobin is unable to bind with or carry enough oxygen, then the patient can suffocate. In addition to oxygen, other molecules can bind to hemoglobin. For example, hemoglobin can bind with carbon monoxide to form carboxyhemoglobin. When other molecules bind to hemoglobin, the hemoglobin is unable to carry oxygen molecules, and thus the patient is deprived of oxygen. Also, hemoglobin can change its molecular form and become unable to carry oxygen, this type of hemoglobin is called methemoglobin.
Pulse oximetry systems for measuring constituents of circulating blood have gained rapid acceptance in a wide variety of medical applications including surgical wards, intensive care and neonatal units, general wards, home care, physical training, and virtually all types of monitoring scenarios. A pulse oximetry system generally includes an optical sensor applied to a patient, a monitor for processing sensor signals and displaying results and a patient cable electrically interconnecting the sensor and the monitor. A pulse oximetry sensor has light emitting diodes (LEDs), typically at least one emitting a red wavelength and one emitting an infrared (IR) wavelength, and a photodiode detector. The emitters and detector are attached to a patient tissue site, such as a finger. The patient cable transmits drive signals to these emitters from the monitor, and the emitters respond to the drive signals to transmit light into the tissue site. The detector generates a signal responsive to the emitted light after attenuation by pulsatile blood flow within the tissue site. The patient cable transmits the detector signal to the monitor, which processes the signal to provide a numerical readout of physiological parameters such as oxygen saturation (SpO2) and pulse rate.
Standard pulse oximeters, however, are unable to provide an indication of how much hemoglobin is in a patient's blood or whether other molecules were binding to hemoglobin and preventing the hemoglobin from binding with oxygen. Care givers had no alternative but to measure most hemoglobin parameters, such as total hemoglobin, methemoglobin and carboxyhemoglobin by drawing blood and analyzing it in a lab. Given the nature of non-continuous blood analysis in a lab, it was widely believed that total hemoglobin did not change rapidly.
Advanced physiological monitoring systems utilize multiple wavelength sensors and multiple parameter monitors to provide enhanced measurement capabilities including, for example, the measurement of carboxyhemoglobin (HbCO), methemoglobin (HbMet) and total hemoglobin (Hbt or tHb). Physiological monitors and corresponding multiple wavelength optical sensors are described in at least U.S. patent application Ser. No. 11/367,013, filed Mar. 1, 2006 and titled Multiple Wavelength Sensor Emitters and U.S. patent application Ser. No. 11/366,208, filed Mar. 1, 2006 and titled Noninvasive Multi-Parameter Patient Monitor, both assigned to Masimo Laboratories, Irvine, Calif. (“Masimo Labs”) and both incorporated by reference herein. Pulse oximeters capable of reading through motion induced noise are disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,650,917, 6,157,850, 6,002,952, 5,769,785, and 5,758,644; low noise pulse oximetry sensors are disclosed in at least U.S. Pat. Nos. 6,088,607 and 5,782,757; all of which are assigned to Masimo Corporation, Irvine, Calif. (“Masimo”) and are incorporated by reference herein.
Further, physiological monitoring systems that include low noise optical sensors and pulse oximetry monitors, such as any of LNOP® adhesive or reusable sensors, SofTouch™ sensors, Hi-Fi Trauma™ or BIue™ sensors; and any of Radical®, SatShare™, Rad-9™, Rad-S™, Rad-5v™ or PPO+™ Masimo SET® pulse oximeters, are all available from Masimo. Physiological monitoring systems including multiple wavelength sensors and corresponding noninvasive blood parameter monitors, such as Rainbow™ adhesive and reusable sensors and Rad-57™, Rad-87™ and Radical-7™ monitors for measuring SpO2, pulse rate, perfusion index, signal quality, HbCO and HbMet among other parameters are also available from Masimo.